This invention relates to a composite building module which is similar to monolithic cast concrete modules in outward appearance and use, yet has significant improvements in insulating properties and weight reduction. More particularly, this invention relates to a composite building module having a rigid foam core, such as a rigid urethane polymer foam, encased or encapsulated in a shell made of a hardened mixture of cement and fibers, such as glass fibers.
Because of increased costs in material and labor, the construction industry has come to use prefabricated building modules, for example wall panels, roof decks and the like. A popular form of construction is known as "curtain-wall" construction and involves the use of a structural steel skeleton which is faced with stacked-up, prefabricated or precast panels. Such curtain-wall panels are commonly cast from reinforced concrete and are provided with a surface finish such as a smooth concrete finish or aggregate imbedded into the face of the panels. These panels are extremely heavy, for example a 4.times.8 curtain-wall panel cast from reinforced concrete weights from 1400-1600 lbs., and require heavy construction equipment to install. In addition, these panels provide very poor insulating properties and by themselves are a poor vapor barrier. This necessitates further construction to insulate and seal the stacked-up curtain-wall of precast concrete modules.
The construction industry has long sought improved building elements that will offer advantages in material and construction costs. A laminated structural element is described Muhim patent, U.S. Pat. No. 3,295,278, issued Jan. 3, 1967, as consisting of (i) a preformed plastic foam layer, (ii) one or more covering layers of aqueous binding material hardened to impart the strength required for a structure where the structural element is to be used, and (iii) mechanical means interlocking the foam covering layers into a unitary element. Heat insulation is imparted by the plastic foam layer while the required structural strengths are provided by the covering layer or layers.
In one embodiment a preformed plastic foam layer is sandwiched between two concrete layers which are connected through openings in the foam layer by a multiplicity of concrete dowels thereby interlocking the layers mechanically. In another embodiment, a covering layer of a hardened cement having a reinforcement of "wood fibers" therein is mechanically interlocked by a multiplicity of "micro-dowels" formed by the binder in surface crevices of the preformed plastic foam layer. The so-called "wood-fibers" providing the micro-dowels have a length of 35-50 cm (approximately 14-20 inches).
Another proposal for a laminated insulating panel is set forth in British Pat. No. 1,030,333 and involves a preformed insulating layer which is surfaced on one or both sides with at least two layers of cement between which is embedded a glass fiber fabric web. The insulating or core layer, which can carry a static load, is made from a mixture of Portland Cement, an aqueous plastic dispersion, sand and a lesser amount of waste foam formed when foamed plastic parts are sawed. The covering layers are made of similar mixture without sand using greater amounts of waste foam.
A real problem encountered in making laminated panels using preformed plastic foam cores (e.g., polystyrene foam) is the lack of adhesive bond between the core and the covering layer. Muhim attempts to cope with this by providing a mechanical interlock using dowels or micro-dowels to form a unitary element. He also contemplates an extra bonding film to improve adhesion. In the British patent, the covering layers contain a binder which will provide a bond with the insulating core. The use of like materials in both the core and the covering layers makes this possible.
The present invention provides a monolithic-like building module which is extremely light in weight as compared to precast concrete panels for example, and which has greatly improved insulating and vapor barrier properties per se. Because the present invention utilizes an in situ foamed core, an adhesive interlock between core and shell is formed which is stronger than either material by itself. The chemical foaming reaction that takes place, plus the fact that foaming takes place in an enclosed shell under retention, results in an overall intimate adhesive interlock and a prestressed structure wherein the shell is under tension and the core is under compression. This means that the shell and core are now united together into a monolithic-like structure that has far greater strengths (because of the overall adhesive interlock) than prior laminated panels using preformed foam plastic cores, and, at the same time, is light in weight and has excellent insulating and vapor barrier properties.